166 MEMOIRS OF THE CARNEGIE MUSEUM 
The specialization of certain parts of the skeleton of S. fossor conclusively proves 
that its ancestors had long been a divergent branch from the true forerunners of the 
family Castoride. At the present time I cannot confidentially point to any living 
rodent of which Steneofiber fossor might be the ancestor. That our fossil shows 
highly developed fossorial characters, is clearly evident from the study of the 
skeleton. It is plain that the beaver bears no close relation to it, so far as the 
structure of the limbs is concerned. The long fore-arm, the short femur, the long 
tibia, fibula, and pes, and the greatly developed hallux, in the beaver, are not sug- 
gested in S. fossor. 
Steneofiber barbouri' spec. nov. 
This species is founded upon the greater part of a skeleton, which is worked out 
in half relief (Fig. 4), and is still imbedded in its original matrix inside of a weathered 
“rhizome” of a Demonelix. It was found in the same horizon, and only a few hun- 
dred feet from where the type of S. fossor was discovered. To judge from Professor 
Cope’s illustration (‘Tertiary Vertebrata,” Pl. LXIIIL., fig. 22), S. barbouri is of 
approximately the same size as S. gradatus, but differs from this species in having 
much more expanded zygomatic arches, more quadrate molars, larger tympanic 
bullee and occipital condyles, and a much broader occiput. 
The smaller size of the skull, and other characters, were at first regarded by the 
writer as individual variations, or possibly sexual differences only, which did not 
warrant a separation from S. fossor. However, a systematic study of the dentition 
Gl ee) BC} 
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Fra. 4. Steneofiber barbouri. } natural size. 
and of the cranial characters has been made, which shows such marked differences 
from the preceding species, that a specific separation was deemed proper. So far as 
can be judged from the material at hand, the limbs and feet are apparently very 
little different from those of S. fossor, except that they are of smaller size. The 
! Named in honor of Professor Erwin H. Barbour, in recognition of his highly interesting work on Demonclix. 
